The following is a roundup of the most downloaded episodes of the ECS Podcast in 2017.

1. Steven Chu talks climate and energy

Former U.S. Secretary of Energy and Nobel Laureate, Steven Chu, delivered the ECS Lecture at the year’s 232nd ECS Lecture. Before he gave the talk, he sat down with ECS Executive Director Roque Calvo for an episode of the ECS Podcast.

“I think as a scientist, you have to be optimistic because usually what you’re doing is trying to shoot for the moon,” Chu said during the podcast. “My optimism comes from the fact that you’ve got a whole bunch of very smart people who are focused on all of the technical problems in the world, including sustainability, energy, and climate change.”